A number of techniques and devices are currently available for administering drugs to the respiratory system. Among them, metered dose inhalers (MDI) or dry powder inhalers (DPI) can be used to deliver drug formulations in the form of solid powders. Several powder properties that enhance delivery to the pulmonary system have been identified. For example, it has been found that particles which have a tap density less than 0.4 g/cm3 and an aerodynamic diameter which is between about 1 and 3 microns are well suited for delivery to the alveoli or the deep lung. If delivery to the central or upper airways is desired, particles having larger aerodynamic diameters, ranging for example from about 3 to about 5 microns, are preferred. Furthermore, particles having a geometric diameter greater than about 5 microns are believed to more successfully avoid phagocytic engulfment by alveolar macrophages and clearance from the lungs.
Methods for producing particles having desired characteristics that can be tailored and optimized for delivery to selective sites of the pulmonary system, and in particular to the deep lung, continue to be needed.